This invention relates to a method of controlling the fuel in a hydrogen-fueled engine.
One means of controlling the fuel in a conventional gas-fueled engine is disclosed in Japanese Published Examined Patent Application No. 23703/1990, in which a fuel intake passage is provided separate from the air intake passage and each of the passages is controlled by a throttle valve. Another fuel control means is disclosed in Japanese Published Examined Patent Application No. 43026/1990, in which there are provided, in parallel, a premixed gas passage for feeding air and the fuel after mixing them together and a direct injection passage for directly injecting the fuel into the engine so that the above-mentioned two passages can be used either separately or together depending on the load or the rotational speed.
However, since the throttle valve in the former publication has manufacturing errors and the premixed gas passage in the latter publication has lower adjustment accuracies near the minimum and the maximum opening degrees, it is practically impossible to accurately control the fuel amount. The graphs of FIG. 4(a) and FIG. 4(b) show controllable ranges of the output Ps and the rotational speed Ne by the conventional throttle valve at high and low hydrogen fuel supply pressures Ph, respectively. It is impossible to accurately control the hydrogen amount over the entire control ranges in either of the conditions in which the hydrogen supply pressure Ph is kept constant at a high pressure or in which it is kept constant at a low pressure.
If the hydrogen supply pressure Ph is kept constant at a high pressure, an accurate control can be made in the region A.sub.1 in FIG. 4(a) and therefore it is possible to obtain and maintain a target maximum output Ps max. However, since there is a limit to the minimum area that can be obtained accurately due to the manufacturing errors or the like of the valve system, it is impossible to accurately control a minimum hydrogen supply amount. As a result, the control becomes inaccurate in the low-load region including idling rotation, i.e., in the region B.sub.1 in FIG. 4(a).
On the other hand, if the hydrogen supply pressure Ph is kept constant at allow pressure, a stable control can be made in the region A.sub.2 in FIG. 4(b), but the control becomes unstable in the region B.sub.2 where the load is high and the hydrogen supply amount is subject to limitations. The reason is that, when a curve Pc in FIG. 5 is supposed to denote the change in the cylinder internal pressure P in accordance with the crank rotational angle .THETA.ca, the crank angle .THETA..sub.1 at the point where the hydrogen pressure Ph and the internal pressure Pc coincide is the supply limit and, consequently, the hydrogen supply amount above the low hydrogen supply pressure Ph is restricted.